The hydraulic valve device according to the invention can be generically categorized as one of pilot-operated check valves which interact largely with directional valves and which are used to control a load. To initiate unblocking of the check valve, either an auxiliary pressure is connected via the directional valve, or the activating pressure of the directional valve is used directly. The auxiliary or activating pressure is then used as a striking pressure to open a pilot valve to relieve the back of the shut-off piston. The load pressure in the working port then acts continuously on an annular surface on the shut-off piston and is opposed to the spring force of the now unloaded back. The activation piston of the pilot valve can then be oriented such that after opening of the pilot valve it also presses the shut-off piston in the opening direction. The activation piston of the pilot valve therefore presses from the side of the fluid-carrying, channel-shaped connecting line to the directional control valve on the respective shut-off piston to open a pilot valve from the spring chamber of the shut-off piston into the connecting channel connected to the return of the entire valve device in this operating state.
Therefore, a throttled connection between the load side and the back via which a continuous control oil flow drains via the pilot valve to the low pressure or tank port of the device during unblocking. Then the hydraulic consumer connected to the respective operating port under load decreases by this leakage flow without the possibility of exerting any influence on the control piston with the control slide generally in the form of a control piston. Accordingly, two fundamental control concepts are distinguished:    1. The control oil is routed into the return channel of the hydraulic device via the control piston. In the neutral position, the control piston establishes throttled relief to the shut-off piston so that it can be placed clearly on its pertinent valve seat without an oil volume being clamped between the valve seat and the control piston. For unblocking at very low loads, the throttled relief must be opened as far as possible so that the load pressure can also lift the shut-off piston. To be able to cover all conceivable load cases, major relief must be chosen which leads to the minimum speed being high when starting up with high loads. This operation is perceived as being unsafe.    2. The control oil is connected past the control piston directly to the leak port or a return port R. The relief throttle on the control piston for the shut-off piston can be chosen to be very small because relief of the back of the shut-off piston is independent of precision control of the control slide. However, the large control oil flow through the pilot valve is disadvantageous under high loads.
The smallest required lowering flow can be assumed to be about 1 l/min. The leakage flow, depending on the design and level of the load pressure, can assume a multiple thereof and thus is no longer acceptable. In particular, the connected machine can no longer be controlled with sufficient precision in the precision control range at high pressures.
In practice, various solutions are known for actuating the activation piston on the pilot valve. Mutual striking is mechanically simple under the action of the inflow pressure. However, for leading loads, the inflow pressure can collapse, and a cycle of closing and opening of the shut-off piston begins, accompanied by jerky movements of the connected hydraulic device. Improvement of operation yields an opening pressure independent of load in the form of the activating pressure for the control piston or control slide. This structure, however, leads to complicated channel routing within the valve device, and the activation piston sitting in the middle of the valve has a long control axis. This structure is accompanied by an increase in the overall size of the valve (WO 2006/105765 A1).
DE 199 19 014 A1 discloses another valve device with a pilot-controlled check valve for activating two working ports. In this known solution, the working pressure of the working port, which is under the inflow pressure, presses on the check valve of the opposite side. In the case of the leading loads, the inflow pressure then drops to the atmospheric pressure, and the striking pressure can collapse. As a result, the check valve closes, and the hydraulic consumer can shut down. In this case, the inflow pressure in turn rises spontaneously, and the check valve opens and accelerates the load until it leads again. The described control period then starts again from the beginning.
U.S. Patent Publication No. 2002/0029810 A1 discloses a valve device in which unblocking is initiated via the control piston. A pilot valve lying transversely to the axis of the control piston is used. The pilot valve arranged transversely in this way must be connected to the assigned connecting lines in a mechanically difficult manner that increases the valve installation height by a considerable amount. To increase production reliability, that pilot valve is supported in an independent sleeve of the valve device.
DE 10 2005 033 577 A1 describes in turn pilot valves which are mechanically struck. To reduce the transverse force on the control piston, the pilot valves are not axially actuated, but are tilted in the manner of a pivoting motion. Mechanical unlocking is ready for operation in a possible failure of the hydraulic energy. The technical mechanical effort for triggering the pilot valves, however, is considerable, especially because an additional attachment housing must be provided which bears the pilot valves and a thin connecting bore must be routed from the respective check valve to the opposite side.
DE 103 25 294 A1 discloses a generic valve device in the manner of a hydraulic control arrangement for activation of a consumer independently of the load. The valve device has a housing section, preferably made as a valve disk, in which a continuously adjustable directional valve controls the flow of the pressurized fluid to the consumer and to which an individual pressure compensator is assigned. At least one shut-off valve is located in the flow path of the pressurized fluid between the directional valve and the consumer and can be unblocked to enable flow of the pressurized fluid from the assigned consumer port. Via a replenishment valve, pressurized fluid from the tank can be replenished when the consumer is undersupplied. In the known solution, the shut-off valve is piloted via a pilot valve whose axis runs perpendicular to the axis of the directional valve. The shut-off valve is located axially parallel to the directional control. The pilot valve then is mechanically openable via a valve slide of the directional valve. Because the axis of the pressure limiting and replenishment valve runs perpendicular to the axes of the directional valve and of the pilot valve, the known solution is characterized by particular compactness, with all essential components necessary in a LUDV system being accommodated with minimum installation space.